There is likely an app or piece of software you love precisely because it solves a problem you despise.

Perhaps it's Mailbox, the mobile email client that delights with its blend of functionality and aesthetics, or Sunrise, the calendar app whose citrus color scheme and clutter-free design help it rise above the default app on your smartphone.

The newest addition to the family of software prized for making life's most frustrating productivity and communication problems melt away on occasion is Slack.

The service -- available on Web browsers or as an app for Mac and Apple's iOS and Google's Android platforms -- is a blend of Facebook and instant messenger. It's not a social network but a tool for businesses that enables employees to chat, share links, message one other, and search the entire database of company communication. It has a free tier, but customers can pay a fee of $7 per user to access the full feature set.

Slack isn't exactly a novel idea. Yammer, Convo, HipChat, Trello, and Socialcast do the same. The list of "Facebook for work" ventures goes on and on. And the communication problem that Slack solves is something neither a Snapchat-using teenager nor a software-illiterate elder will ever in a million years care about.

Instead, Slack is turning heads because it's more successful as an enterprise service than most breakout consumer mobile apps are. Even its creator isn't sure what's causing the boom.

"Slack addresses a huge problem that nobody even knows is real," said Stewart Butterfield, founder of TinySpeck, the company behind Slack. Butterfield rose to tech industry fame when he and fellow co-founder Caterina Fake sold their Flickr photo-sharing site to Yahoo in 2005 for more than $22 million.

When it comes to Slack, numbers don't lie. The service is six months old, yet has more than 140,000 daily active users, with nearly 29 percent of that base are paid users. That's resulting in $3.5 million in projected annual revenue, and the amount is increasing by $1 million every six weeks. Slack is used by more than 33,000 teams around the globe, and 93 percent of teams that start using Slack stick with it. The company has no sales or marketing team.

"It's impossible for us to know what it is that caused the growth," Butterfield admitted. "It's true that across the board there's room for all kinds of innovation especially when people don't expect it."

That's one of the few lights of clarity breaking through Slack's hard-to-decipher popularity. People are happily surprised when a problem is solved in elegant fashion, even when the problem is some mutant conglomerate of office shortcomings and roadblocks, Butterfield figures. It helps explain why something as unmoving as a company chat room could lead customers like BuzzFeed and Gawker Media to half-jokingly list Slack as a company perk. As in, "Work for us and you won't become a Sisyphean slave to your email inbox and the chase after overlooked G Chats."

Butterfield summarizes the utility with an example of an employee switching jobs. "You get a new email address and your inbox is empty, and yet yesterday there was thousands of messages sent by people on your team, the month before tens of thousands. The last decade? Millions of messages," he said. "None of that is accessible to you, all that institutional knowledge is fractured."

Centralizing the means of communication is Slack's purpose. "Every team will have some centralized system of communication in the next 10 years," Butterfield added.

When it comes to its distinct problem-solving ability, Slack's goal is less about tackling specific issues like cutting down inter-office email or trying to avoid having your team use a half-dozen different communication tools at the same time. Slack, like most modern software nowadays, drives by the rules of a post-iPod era: app users don't necessarily know what life is like without its inefficiencies until you show them, even if it means adjusting.

"Every team will have some centralized system of communication in the next 10 years."

Stewart Butterfield, Slack founder

"There's a set of features that people want that they don't even know that they want," Butterfield said. "They weren't asking of them but when they get them, they like them." Those include Slack's ability to format links with the most relevant information, like an article link that displays the headline, writer byline, and publication name. Slack also integrates with services like Google Drive and Dropbox while moving most of their functionality into the app itself. Drop a Google Doc into the chat, for instance, and users can view and comment on changes without leaving Slack.

Slack is emoji- and GIF-friendly, something you wouldn't necessarily think of as conducive to company culture until Rick from marketing can't stop posting Beyonce clips and brings the office a little closer over a shared love of looped nonsense dug up from Reddit. The gaming site Polygon even rigged up a way to battle Pokemon from the titular role-playing classic within Slack using hashtags.

Stewart Butterfield, cofounder of Flickr and founder of Slack.
TinySpeck

There are some things it doesn't do. It does not allow a Facebook-style posting that would let users read something hours old and comment on it, and Slack doesn't support posting via email to forward messages that land in your inbox. (Butterfield said Slack is working on the latter.) The company is also working on threading messages like Twitter now does with @ replies that would group together a conversation in an easy-to-read cluster. That would help maintain both the real-time communication element Slack thrives on while giving a semblance of continuity to the flow of messages that can sometimes be hard to weed through unless you're a power user of its search function.

Slack isn't for everyone. The software is indeed used by a companies full of hip, modern Web natives like Airbnb, Urban Outfitters, and Blue Bottle Coffee, but Slack calls everyone from Dow Jones and The Times of London to Sony and HBO customers as well. Some organizations, however, don't mesh well with Slack, and some never will, Butterfield concedes.

"Imagine a real estate office. They are all on the same team but most realtors spend most of their time talking to their clients instead of each other," he said. "Then there's organizations for whom Slack would be great, but they're too locked down from an IT perspective." That's not exactly dampening his spirits, though, given that Slack is good at solving problems with a speed that's causing investors and interested acquirers to dial Butterfield every week.

"Even if we have tens of millions of users," Butterfield added, "that will still make us one of the most successful software companies in the world."